The band of 6 GHz or less convenient for mobile communication systems (VHF, UHF, low micro band) is now used densely for communication by the third generation mobile phone, wireless LAN and the like and the tight condition of frequency is getting increasingly serious. Under such a situation, in order to use effectively and efficiently radio wave whose availability is getting increasingly stringent and to obtain allocation of frequency band necessary for mobile communication for which the needs are high, a technology for realizing a high-level common use of radio wave among systems using a plurality of radio waves such as mobile communication is sought after.
On the policy level, the “e—Japan priority plan—2004” (June, 2004) established by the IT Strategy Headquarters of the Ministry of Internal Affairs and Communication of Japan sought a technology for realizing “the putting to practical use by 2011 a radio communication system for establishing an optimum communication environment by determining precisely the requirements of the radio wave environment and the applications used, and flexibly selecting frequency band, modulation method, multiplexing method and the like.
In order to realize these requirements, the idea of “cognitive radio” for recognizing the state of the radio and controlling the resources of radio systems depending on the state thereof was published in 1999 (Mitora, “Cognitive radio for flexible multimedia communications”, 1999 IEEE Int Workshop on Mobile Multimedia Communications Digest (November 1999), and Mitora, “Cognitive Radio: Making Software Radios More Personal”, 19999 IEEE Personal Communication, vol. 6, No. 4 (1999)). However, there are a variety of approaches for realizing cognitive radio, and the parties concerned are studying the problem at present.
For communications using a multimode radio system, a technology in which the base station side decides the radio system and the base station side designates the radio system to the terminal side has been proposed (JP 2003-169379 A, JP 2005-20477 A).